JWST + ALMA ubiquitously discover companion systems within $\lesssim18\,$kpc around four $z$$\approx$3.5 luminous radio-loud AGN

TL;DR

This study uses JWST and ALMA data to discover multiple companion systems around four high-redshift radio galaxies, shedding light on galaxy interactions and AGN activity at cosmic noon.

Contribution

First detection of kpc-scale companions around $z\sim3.5$ HzRGs using combined JWST and ALMA observations, revealing potential minor mergers and their impact on AGN activity.

Findings

Approximately 12 companion systems within 18 kpc identified.

Companions show evidence of disk rotation and complex motions.

Estimated dynamical masses suggest minor merger scenarios.

Abstract

Mergers play important roles in galaxy evolution at and beyond Cosmic Noon ($z\sim3$). They are found to be a trigger of active galactic nuclei (AGN) activity and a process for growing stellar mass and black hole mass. High-$z$ radio galaxies (HzRGs=type-2 radio-loud AGN) are among the most massive galaxies known, and reside in dense environments on scales of tens of kiloparsecs to Megaparsecs. We present the first search for kpc-scale companions in a sample of four $z\sim3.5$ HzRGs, with many supporting datasets, using matched 0.2" resolution ALMA and JWST/NIRSpec integral field unit data. We discover a total of $\sim12$ companion systems within $\lesssim18\,$kpc across all four HzRG fields using two independent detection methods: peculiar [OIII]$4959,5007$ kinematics offset from the main (systemic) ionized gas component and [CII]$158\rm \mu m$ emitters. We examine the velocity fields of these companions and find evidence of disk rotation along with more complex motions. We estimate the dynamical masses of these nearby systems to be $M_{\rm dyn}\sim10^{9-11}\,M_{\odot}$, which may indicate a minor merger scenario. Our results indicate that these companions may be the trigger of the powerful radio-loud AGN. We discuss the roles of the discovered companion systems in galaxy evolution for these powerful jetted AGN and indicate that they may impede jet launch and deflect the jet.